Polyolefins, particularly polypropylene, have inert surfaces thus are not readily bonded by other materials. Various surface treatments such as flame oxidation, corona discharge and chemical etching have been used to activate these surfaces with some measure of success. This invention concerns articles comprising polymers bonded to polyolefin surfaces, particularly to untreated polyolefin surfaces and most particularly to the difficult to wet untreated polypropylene surfaces. These polymers comprise mer units having comparatively non-polar and non-polarizable groups, other than small groups, extending from the polymer backbone. In various embodiments the adherent vinyl polymers, or bonded polymers, appear as adhesive coats, tiecoats, topcoats or as components of these. Articles exemplifying embodiments of this invention include nonwoven fabrics, woven fabrics and flocked fabrics, all comprising polyolefins and the adherent polymers; laminates of polyolefins and other materials; and decorated polyolefins in which the pigment, dye or other decoration is bonded by the adherent polymer.
It is known to employ certain, relatively expensive, chlorinated polymers as primers to enhance the bonding of materials to untreated polyolefin surfaces. It may be speculated that these polymers are actually a form of chemical etching by means of their slow release of strong acid or strongly oxidizing materials. Chlorinated mixtures of a hydrocarbon resin and polyethylene are taught for use as primers and paint and ink additives for improving adhesion of coatings to polyolefin, by Etter in U.S. Pat. No. 4,070,421. Chlorinating carboxyl-group-containing polyolefins to form primer coatings for untreated polyolefin substrates is taught in U.S. Pat. No. 3,579,485. Menikheim et al., in U.S. Pat. No. 3,380,844 teach the coating of polyolefin film by a polymer of vinylidene chloride, a (meth)acrylate ester and (meth)acrylic or itaconic acid. The polymers are recited as having non-strippable adhesion to polyolefin substrates. Acrylic esters having alkyl groups containing more than two carbon atoms were found to be not entirely satisfactory in these polymers.
Polymers other than chlorinated polymers have also been adhered to polyolefins. Agouri et al. teach a process for chemical modification of polyolefins by grafting polar monomers onto the polyolefin by means of a free radical generating material, in U.S. Pat. No. 4,080,405, to produce a polyolefin surface having improved wettability. MacArthur, in U.S. Pat. No. 3,394,029, teaches the coating of polyolefin surfaces by polymers of certain terpene acrylates and N-terpene acrylamides for improved adhesion of conventional lacquer topcoats. Chancler et al., in U.S. Pat. No. 4,014,645, teach the enhancement of dye receptivity of polyolefin materials used in fabric manufacture by coating the polyolefin with a self-curing polymeric binder containing a quaternary ammonium salt. Emmons et al., in U.S. Pat. No. 4,097,677, disclose certain radiation curable coatings, useful to coat some polyolefins; the coatings comprising monomeric unsaturated esters of glycol monodicyclopentenyl ethers. In British Pat. No. 1,177,199, there is disclosed nonwoven webs containing a major amount of polypropylene fibers bonded with a binder comprising vinyl acetate, ethylene and an unsaturated N-methylol amide or an alkyl ether thereof. It is pointed out that "as is well known, it is extraordinarily difficult to bond polypropylene to itself or to other materials." (page 1, line 53). Robinson et al., in U.S. Pat. No. 3,241,662, teach the preparation of a roll of biaxially oriented polypropylene film having an activated surface and adherent to the activated surface a pressure sensitive adhesive which does not adhere to the untreated surface. The polymer is a polymer of about 55 to 95% of an alkyl ester of acrylic or methacrylic acid with the alkyl group preferably having 6 to 12 carbon atoms, up to 12% of an unsaturated carboxylic acid or unsaturated aliphatic amide and various other comonomers. Cantor et al., in U.S. Pat. No. 3,258,443, describe a latex which may be used to deposit a pressure-sensitive adhesive on polyethylene and polypropylene. The latex is prepared from 1 to 45% vinyl acetate, 50 to 98% of an alkyl acrylate having an alkyl group of between 4 and 10 carbon atoms (several acyclic alkyl groups are named) and 1 to 5% of an unsaturated carboxylic acid. The alkyl group containing 4 to 10 carbon atoms preferably contains at least 6 straight chain carbon atoms and most preferably is the 2-ethylhexyl group. James et al., in U.S. Pat. No. 3,519,531, disclose certain copolymers of ethylene and vinyl esters of alkenolic acids and alkyl esters of acrylic or substituted acrylic acid, for coating polypropylene film. Taft et al., in U.S. Pat. No. 3,887,738, teach hot melt compositions comprising a copolymer of ethylene and vinyl acetate and/or alkyl acrylate useful as an adhesive for the back sizing of tufted carpets which may comprise polypropylene backing materials. Two patents to Baatz et al., U.S. Pat. Nos. 3,931,087 and 4,012,560 teach the use of copolymers of a sulfonic acid and esters of acrylic or methacrylic acids as pressure sensitive adhesives which are adherent to a number of surfaces including polyethylene and polypropylene. Peterson, in U.S. Pat. No. 3,524,795, teaches layered barrier packaging films employing polyolefin outer layers and a gas barrier inner layer bonded together by adhesives such as chlorinated polyethylene, a copolymer of ethylene and vinyl acetate, and copolymers of ethylene and certain lower acrylates.
There is taught, in the present invention, articles comprising polymers surprisingly adherent to polyolefin surfaces especially untreated polyolefin surfaces and more particularly untreated polypropylene surfaces. Untreated polyolefins, particularly untreated polypropylene have not been commercially employed to the extent desired because of the difficulty in finding adhesive compositions suitable for coating or adhering other materials to this polypropylene. The present vinyl addition polymers are surprising in giving excellent adhesion to untreated polypropylene without the use of chlorinated or other halogenated polymeric materials. They also make unnecessary cumbersome and expensive pretreatments such as corona discharge, heat and flame treatments, treatment with chemical agents such as ozone, halogens, chromic acid or bombardment by electrons.